Electromagnet



March 31, 1959 l D. I. BoHN 2,880,382

ELECTROMAGNET Filed April 14. 1953 2 Sheets-Sheet l IN VEN TOR. l 70 /ga [4/ I8/ /39 /80 .Po/waa .ZT Bax/lv D. l. BOHN ELECTROMAGNET March 31, 1959 2 Sheets-Sheet 2 Filed April 14. 1953 INVENTOR. .DOA/mali Zay/v United States Patent O 2,880,382 ELECTROMAGNET Donald I. Bohn, Pittsburgh, Pa.

Application April 14, 1953, Serial No. 348,658

14 Claims. (Cl. 317-165) My present invention relates to an electro-magnet and more particularly it relates to an electro-magnet whose armature moves as a function of the energizing current.

Up to the present day, electro-magnets had only two electrical positions, one in which the armature of the magnet is at a certain position away from the magnet and the second in which the armature of the magnet is in direct contact with-the magnet itself.

Many mechanical devices have been constructed to permit the armature of the magnet to occupy intermediate positions between the above-mentioned positions. In some types of relays, for example, one intermediate position was made possible by rather complex mechanical devices in conjunction with biasing means.

More specically, in conventional electro-magnets if an adjustable voltage is applied to its coil, nothing will happen until a suicient flux density exists in the two air gaps to lift the armature of the magnet away from its non-operative position and in the case of relays, for example, against the tension of a spring.

In this case, however, as soon as the initial motion of the armature occurs, the reluctance of the entire magnetic circuit is appreciably reduced, and the ux further increases because of the decrease in air gap between the armature and the magnet. This cumulative action makes it impossible to have an intermediate position for the armature and, therefore, will go to its operative position, in other words, in direct contact with the electro-magnet.

As above mentioned, such a conventional electro-magnet whether made of laminations or of solid construction has only two positions, the open and the closed, and any schemes used in the art up to the present time have always been very complex andA have further resulted in extreme weakening of the magnetic pulling force.

The mechanical devices used for obtaining the intermediate position between the open and the closed position of a conventional electro-magnet have to build up mechanical counter forces faster than the increase in magnetic forces because of the increasing ilux due to the reduction of the air gap between the armature and magnet.

This problem becomes important, for instance, in voltage regulators which require a magnet whose armature takes different positions corresponding to different values of ampere turns. Up to the present day, this was obtained by practically eliminating all the iron in the circuit except that in the armature which, of course, greatly weakens thte pulling force of the magnet as compared with watts required.

This is undesirable and has resulted in the necessity of making such voltage regulators employ a very delicate mechanism since the force versus distance characteristic of the armature is extremely poor. The above is only one instance in which this problem arises.

Other fields in which this problem arises are, for example, in valves where butterfly valves must sometimes occupy an intermediate position between the open and the closed position. Another eld is in electric brakes which up to the present time had only two positions, an

on position and an oi position. This makes electric brakes unsatisfactory since in many applications it is desirable to have a variable braking action, function of the current llowing in the coil of the electro-magnet.

My novel electro-magnet overcomes the above-mentioned diiculty by providing a magnet in which the ilux increases practically independently of the air gap between the armature and the magnet itself, in other words, in which the flux increases only as a function of ampere turns or the current owing in the energizing coll.

In one embodiment of my present invention, a U- shaped stationary electro-magnet structure is provided with laminations in the horizontal section of the U-shaped structure. These laminations are so arranged that the ux entering the horizontal core from any of the two vertical cores will progressively go through the insulating layers between laminations in the horizontal core.

Vertical cores do not necessarily have to be made of laminations, but they could also be made of solid material.

In this embodiment of my novel invention, the armature of the electro-magnet is pivoted at one end so that it may rotate between an open position and a closed position, the open position corresponding to the maximum air gap position, the closed position corresponding to zero air gap.

A coil is wound around the center horizontal leg and a variable source of is applied to the coil. The armature is biased by means of a spring toward its open position so that the pulling force of the electro-magnet moves the armature from its open position against the bias of this spring.

The lamination used in the center horizontal core can, for example, be ofthe kind used in transformers.

When the voltage applied to the energizing coil of my novel electro-magnet is zero, the armature is in its inoperative or open position, that is, an air gap exists between the stationary portion of the electro-magnet and one end of the armature.

If now the voltage is increased, the current owing in the energizing coil will also increase producing a magnetic ilux in the magnetic circuit consisting of the stationary magnet, the air gap between the magnet and armature and the armature itself.

Because of the particular disposition of the laminations in the center leg of thestationary magnet as the lux owing through the magnet increases, it will first ow only Vthrough the lamination that is nearest or in closer contact to the two vertical legs. When saturation for this lamination is reached, the excess flux will jump from the above-mentioned lamination to the next one since because of saturation the first lamination cannot carry more llux than the one corresponding to the at portion of the saturation curve.

If the voltage applied to the energizing coil is increased further and further, the ilux will reach a value at which it will produce a suicient magnetic pull for moving the armature toward the stationary magnet. Under this magnetic pull or force, the armature starts moving toward the stationary magnet.

In other words, the armature as it moves toward the magnet will decrease the air gap existing between the `armature and the magnet itself.

As previously mentioned in a normal type magnet, a cumulative action takes place with a result that the armature will slam against the stationary magnet.

In my present invention, on the other hand, a decrease in the air gap between the armature and the magnet will not cause suttcient cumulative effect to take place. In fact, when the armature moves toward the magnet, thus decreasing the air gap between the armature and magnet, the magnetic ux owing in this circuit attempts to rise because of the decrease in the reluctance of its path due to the decrease in air gap, but as the fiuX increases because of these reductions in reluctance and rst saturates, for example, the fourth lamination of the horizontal or center leg of the U-shaped magnet, it will lind in its path toward the next lamination the air gap (although air is here mentioned it can also be a suitable dielectric) which tends to increase again the reluctance of the magnetic circuit.

To summarize the above, because of the particular disposition of the lamination in the center leg of the U-shaped magnet, as the air gap between the armature and the magnet decreases because of the increase in ux produced by the increase in energizing current, then additional reluctance is introduced in the form of air or dielectric gaps between laminations of the center leg of the U-shaped magnet.

From this Ait is easily seen that by correctly choosing the vlamination material so that it may have a desired saturation curve and by correctly spacing the laminations of the center leg of the U-shaped magnet any form of relationship between the current in the energizing coil and the air gap between the armature and magnet can be obtained.

Up to now, only current of the energizing coil was K mentioned, but, of course, instead of current it would be just as suitable to talk in terms of kva. of the energizing coil.

While the above-mentioned magnet was described for a direct energizing voltage, the same type of magnet could be used when the energizing voltage or current is sinusoidal.

The main object of my present invention is the provision of means whereby the armature of an electromagnet can occupy any position between two limiting ones.

Another object of my present invention is the provision of means whereby the magnetic pulling force of a magnet can become independent of the air gap between the magnet and the armature.

A further object of my present invention is the provision of means whereby any relationship between the magnetic pulling force and energizing kva. can easily be obtained.

Another object of my present invention is the provision of means whereby relays having more than two positions can be built economically and with the same labor that is now used for constructing relays having only two positions.

The foregoing and many other objects of my invention will become apparent in the following description and drawings `in which:

Figure 1 is a perspective view o'f my novel electromagnet.

Figure 2 is a side view of Vthe electro-magnet of 'Figure vl.

'Figure 3 is a schematic diagram of an engine using my present invention.

'Figure 4 is va detail drawing of the engine of the controlling mechanism for the engine of Figure 3.

Figure 5 is a plot vof desired and actual pressure versus kw. for lthe engine of Figure '3.

Referring to Figures l and 2 showing one embodiment of my Apresent invention, the stationary magnet is a i-shaped structure consisting of legs 11 and 12 breached by a transverse or center piece 14. A spool 15 ksurrounds the center portion of the transverse piece 14.and carries wound around itself a coil 18 having terminals 19 `and 20.

The two side legs 11,and 12 in this particular embodiment are made of a number of laminations 21 of magnetic material. Laminations 21 are separated from each other by -an insulating coat 22 similar to the one used in transformer laminations. v A pair of rivets 24 serves to keep together each stack of laminations forming legs 11 and 12, respectively.

As seen in Figures 1 and 2, the laminations forming side legs 11 and 12 are parallel to the surface of the drawing in Figure l and perpendicular to the surface of the drawing in Figure 2 and in both cases laminations 21 forming side legs 11 and 12 are vertical.

As for laminations 21 forming the center piece or member 14 which are similar to those on side legs 11 and 12, they are horizontal and perpendicular to the drawing sheet in Figure l and also perpendicular and horizontal in Figure 2. Laminations 21 forming center piece 14 are secured together and to the side legs 11 and 12 in any suitable way.

The above-described disposition of laminations produces this elect: The magnetic llux in side legs 11 and 12 will distribute itself more or less evenly in all the laminations 21 forming side legs 11 and 12. The magnetic flux in center piece 14, on the other hand, will first flow through laminations 21a.

Then when lamination 21a is completely saturated, the extra portion of the llux will jump across the air gap between laminations and llow in lamination 2lb.

This process is repeated until the llux flowing through the magnet 10 occupies a sufficient number of laminations 21a, b, etc. in the center of leg 14.

Armature 30 of electro-magnet 10 consists also of a number of laminations 31 separated from each other by an insulating coat 32 similar to the laminations and the insulating coat, respectively, 21, 22 of side legs 11 and 12, the only difference being in their physical shape.

Laminations 31 and 32 are held together by a frame 35 consisting of side members 36, 37 holding between them by means of rivets 39 all laminations 31. Frame 35 is provided at one end with an opening 40 to receive a pin 41 around which armature 30 is rotatable. On the other end of frame 35 is a pin 42 to which a biasing spring 45 is secured. Biasing -spring 45 is in this case a tension spring to tension armature 30 away from the stationary electro-magnet 10.

Therefore, spring 45 is secured to a suitable stationary surface 47. A stop 50 secured to another stationary surface (not shown) serves to limit the travel of armature 30 under the tension of spring 45.

Laminations 31 of armature 30 are shown in parallel to the drawing sheet in Figure 1 and perpendicular to the drawing sheet in Figure 2.

Although side legs 11 and 12 and armature 30 were above described as made of laminations 21, they are really not necessary for vside legs 11 and 12 and armature 30. Solid blocks of suitable material would serve just as well. The only portion of this electro-magnet 10 which must have laminations 21 and in which laminations must occupy a certain pre-selected position with respect to'legs 11 Yand 12 -is the center piece `14 as will be clear later on in this description.

In the description of the operation of this novel electrornagnet 10, it will now be assumed that a variable D.C. supply 60 is applied across terminals 19, 20 of energizing coil 18. At the beginning, in other words when the voltage of the supply 60 is zero, no current will llow in coil 1S and, therefore, no ux will exist in the vmagnetic circuit consisting of stationary magnet 10, air gap 65, armature 30 and air'gap 66.

If now the voltage of power supply 60 is increased, a current is produced in coil 18 which in its turn produces a flux in lthe abovefmentioned lmagnetic circuit 10-65-30-66. This flux, of course, increases with the lincreasing voltage of the vvariable supply 60, but

`while it will lbe more kor less evenly distributed in lthe side legs 11 and 12, air gaps 65, 66 and armature 30, it will start Vby llowing first in the lamination 21a of center leg 14, will then ow in laminations 21a and 2lb after saturation of lamination21a.

lAt saturation of llamination`21b, if the lux is further increased by increasing the voltage of the supply 60, the extra ux will ow in lamination 21e until this lamination becomes also saturated. This process continues until the correct number of laminations 21 of center leg 14 are saturated by the flux produced by coil 18.

In the magnetic circuit formed by magnet 10, air gaps 65, 66 and armature 30, the reluctance at the open position of armature 30 (the position shown in Figure 1) is fairly high due essentially to the large air gap 65 between stationary magnet 10 and armature 30.,

As the voltage of variable supply 60 is increased further and further, the ux flowing in magnetic circuit -65-30-66 will continue to increase until it produces suflicient magnetic force or pull to pull the armature 30 in the direction of stationary magnet 10 against the bias of spring 45. Under such a magnetic force, armature 30 will rotate toward its closed position (shown dotted in Figure l), thus decreasing the air gap 65 between stationary magnet 10 and armature 30.

At the same time, of course, gap 66 is also slightly reduced but since of the two effects the one at 65 is more important, we shall consider the air gap decrease at 66 to be negligible in comparison to the change in air gap 65. I

As above-mentioned, air gap 65 is reduced because of the motion of armature 30, but a reduction in air gap 65 means a reduction in the reluctance of magnetic circuit 10-65-30-66 and would, therefore, attempt to bring about a larger value of iiux.

It is well-known, in fact, that the flux owing in a magnetic circuit is directly proportional to the ampere turns and inversely proportional to the reluctance of the circuit itself.

If, therefore, the reluctance of the circuit is decreased due to a decrease in air gap 65, the ampere turns remaining constant, the flux will tend to increase. As the ux tends to increase because of the reduction of air gap 65, a portion of it will have to move from say lamination 21e to lamination 21d in center leg 14, the above-mentioned portion of llux being the `extra flux after lamination 21e is completely saturated, but if this extra flux jumps to the next lamination 21d, two more air gaps will be introduced in the magnetic circuit 10- 65-30-66, the two air gaps being the air gap between laminations 21C and 21d at the end of center piece 14 near leg 11 and the air gap between laminations 21d and 21C at the other end of center piece 14 where the flux was assumed to flow in a clockwise direction although the direction of flow is quite unimportant since as previously mentioned my novel electro-magnet will also operate with a sinusoidal ux.

The introduction of the air gaps between laminations 21C and 21d essentially increases again the reluctance which had been decreased because of theldecrease of air gap 65 with the result that the total reluctance of the magnetic circuit 10-65-30-66 is not decreased as much as it would have decreased if air gap 65 had been decreased without the introduction of the vadditional air gap between laminations 21e` and 21d.

Actually by introducing dielectrics between laminations 21c and 21d and so on or by appropriately separating laminations 21e, 21d, etc., it is possible to obtain any desired relationship between ampere turns of the energizing coil 18 and thedisplacernents 'of' armature 30 with respect to stationary magnet 10.

Since as above explained the total reluctance of the magnetic circuit 10-653066 does not decrease at all or does not decrease as fast as the decrease in reluctance due to the decrease of air gap 65, armature 30 will not undergo the cumulative action that is known to occur in relays or electro-magnets made of solid material, but armature 30 will move in a certain relation with respect to the KW applied to the energizing coil.

Referring next to Figures 3 and 4 showing a scavenging air control system using my novel electromagnet, the scavenging air is blown by means of a centrifugal or other type of blower 71 into the engine (not shown) which in this case may be, for example, a gas burning internal combustion type engine having conventional spark plug ignition in which, therefore, it is necessary to vary the amount and, therefore, the inlet pressure of the scavenging air supplied to the engine cylinder by means of the above-mentioned blower 71.

Inlet air to the blower 71 enters through conduit 70, and the pressure to the engine may be varied by means of butteriiy valve 73.

In this particular case, the blower is assumed to be driven at a constant speed so that the amount of air and also the inlet pressure is varied as desired by means of a buttery valve 73 operated by a small motor 75 through a gear box 76.

Controlling the operation of motor 75 is my novel relay in a form modified from that shown in Figures 1 and 2. Relay or electromagnet 80 is energized responsive to the load of the engine and serves to actuate the motor 75 in the reverse or in the forward direction. Motor 75 can be in this case, for example, a small synchronous motor operating at 75 r.p.m.

ReferringV now to Figure 5, the desired curve shows the correct relation between kilowatt load on the engine of Figure 3 and the pressure in p.s.i. of the scavenging air at the entrance of the engine 86. The second curve 87 starts at the same point as the desired curve 85 and is a square curve in that it is the representation of a conventional square law.

One of the main reasons why the usual relays do not fulfill the requirements of this operation is that if the coil of such a conventional relay is supplied with direct current in proportion to the kilowatt load of the engine, then the force on the. armature of this relay or electromagnet will vary as the square of the current and, therefore, as the square of the load as shown by the abovementioned square curve 87.

The action of this magnet can, of course, be balanced against a substantially frictionless diaphragm actuated by scavenging air inlet pressure and if this square curve 87 could be modified to match the desired curve 85, this trouble would be overcome.

Another objection to using conventional relays is that all conventional electromagnetshave practically all of their magnetic circuits made of iron except the necessary air gap and, therefore, they would be quite unstable. By unstable it is meant that if a good mechanical force is applied to counteract the magnetic force and this mechanical force is left constant, then if the magnetic force is varied it will be found that it will be impossible to so vary it as to stop the armature of the conventional magnet in between the two limiting positions or stops. This is true even though special springs are employed, and there is no simple way of providing a kinematic system which will overcome the inherent weakness of a conventional magnet of this type when it is attempted to use it in this manner.

If such a conventional relay were employed, it would, of course, hold the air pressure quite satisfactorily, but in over to do so it would continually move from one contact to the other and operate the motor forward and backward without a single pause. This is, of course, quite impactical since there is no basic object in operating the motorr continuously as under normal engine conditions the load remains relatively constant for minutes at a time.

In order to introduce the desired stability to conventional relays so that the movable arm or armature can float between two contacts, a modified form of the electromagnet of my invention is used as relay 80 of Figure 3 shown in detail in Figure 4.

Referring, therefore, to Figure 4 showing a crosssectional view of relay 80 of Figure 3, a panel mounted member 101 is machined in circular shape and bolted by means of studs or cap screws 102 to a machined piece of iron pipe 103 which may also be a machined steel cylinder'. A flexible diaphragm 105 of material similar to that which is used in fuel pumps is pinched between surface 101 and one end of cylinder 103 so as to be responsive to the scavenging air pressure acting on diaphragm 105 through opening or pipe connection 107 in the Vside surface of steel cylinder 103. Clamped on this diaphragm 105 by means of clamp 109 are two members 110 and 111 which, therefore, would be pressed in the upward direction in direct proportion to the air pressure supplied at the pipe connection 107.

In order to make the chamber 112 enclosed by cylinder 103 and diaphragm 105 air tight and still permit the introduction of magnetic flux to this chamber 112, a bronze diaphragm 115 is installed on a turned shoulder 117 in the machined steel cylinder 103. The movable armature 120 of the relay 80 consists of a machined steel cup 121 circular in plan view and having cylindrically shaped lower ends 122.

A spacer 125 is located between member 111 and base 127 of cup 120 to separate and space cup 120 from members 111 and 110. The previously mentioned clamp or screw 109 passes through spacer 125 toengage a threaded portion 130 in cylindrical bore 131 in lower end 122 of cup 120 rigidly securing, therefore, members 110, diaphragm 105, member 111 to cup 120.

The particular shape of cup 120 so distributes the uX density owing through cup 120 that the magnetic pull is practically all concentrated at the lower end 122 of cup 120 while the return flux is handled by the large outside circumference 132 of the cup-shaped armature 120.

Members 110 and 111 as well as spacer 125 are madeA of non-magnetic material, preferably aluminum because of its lightness.

In chamber 112 on the other side of bronze disc 115 is a stationary core 139 made of iron and designed so that it rests against the lower side of the bronze diaphragm 115. Iron core 139 is surrounded by a conventional coil 140 wound on the support 141. The coil current is varied in any desirable way in proportion to the kilowatt load on the engine. If possible, coil 140 should be connected in series with the load or it could be a winding in parallel with the conventional shunt so that its current varies proportional with the load.

For this particular case the current used to energize core 139 is the rectied A.C. input to a transductor which is a form of direct current saturating measuring transformer.

On panel 101 is also mounted a member 145 which is engaged by a pin 146. Pin 146 also engages an opening 148 at one end 149 of contact arm v 150. Contact arm 150 is provided at its other end with an extension 151 carrying spherically shaped contacts 153, 154 one on each side of extension 151. Spherically shaped contacts 153 and 154 engage, respectively, stationary contacts 156 and 157 when the contact arm is in the upper position and when the contact arm is in the lower position, respectively.

Clamp 109 serves also to secure through extension 160 of contact arm 150, contact arm 150 to members 110 and 111 and, therefore, to the cup-shaped armature 120 of relay 80. Movable contact arm 150 is also provided at the end near extension 151 with a spring 162 which is a zero load adjustment spring and is simply made so that the relay 80 will provide the desired no load air pressure which in this particular case is about .7 p.s.i. As can be seen from Figure 4, spring 162 is secured at one end to movable contact arm 150 through hook 163 and at the otherend to a stationary portion of relay 80 through a screw 165. Rotation of screw 165 will produce adjustment of the tension of spring 162.

It will first be assumed that the return ux from the bottom of core 139 to the periphery of steel cylinder 103 is taken care of by either a plate or bai of ordinary iron connecting, therefore, the bottom of core 139 and the bottom of Vsteel cylinder 103. In this case the relay (see Figure 3) will quite accurately control buttertly valve 73, but it will do so by continuously oscillating from contact v156 to contact 157 and vice versa (see Figure 4) and, therefore, continuously oscillating the butterfly valve motor 75 and, therefore, the buttery valve itself 73.

As previously mentioned, this very noticeable condition can be overcome bythe use of my novel relay. lf, in fact, a group of laminations stacked horizontally provides a ilux path from the bottom of core 139 to the lower peripheral surfaces of steel -cylinder 103, a construction similar to the one shown in Figures l and 2 will thereby be achieved.

In this particular case the insulating coating between each lamination 170 does not provide enough air gap. Therefore, laminations 170 must be provided with nonmagnetic: layers 171 between each lamination and the next.

Of course, as previously mentioned, a normal insulating varnish on laminations such as lamination 170 is usually sufficient, but on this particular device it was found necessary to insert a .003 inch paper between each lamination in order to provide the proper selective growth o f uX in this laminated assembly.

Lamination 170 can be secured to a steel cylinder 103 by any appropriate means as, for example, non-magnetic screws and core 139 can also be secured to these laminations 170 by a similar non-magnetic screw 181.

-When laminations 170 are thus secured to relay 80 and form a portion of the magnetic circuit of the stationary portion of relay 80, relay 80 immediately performs as desired and when in actual operation movable contact arm 150 would float for minutes in between the two stationary contacts 156 and 157 which as previously mentioned provide the forward and reverse circuit for the buttery valve motor 75.

In order to further approach the desired curve 85 shown in Figure 5, stationary core 139 was modified in shape. ln fact, the outer portion of core 139 is necked out at 186 so that as the flux increases this necked portion 186 becomes saturated offering additional reluctance to the magnetic flux which tends to tip square curve 87 away from its former position to coincide more or less perfectly with the desired curve 85.

In the foregoing I have described my invention solely in connection with specic illustrative embodiments thereof. Since many variations and modications of my invention will now be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein contained but only by the appended claims.

I claim:

1. A magnetic circuit comprising a core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining Sets, the reluctance between said armature and said core decreasing with movement of said armature toward said core gat increasing energization of said coil, the reluctance between the said one set of laminations and said remaining sets increasing at the movement of said armature toward said core, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature toward said core.

2. A magnetic circuit comprising a core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the first laminationof said one of said sets stacked in said perpendicular direction, the reluctance between said armature and said core decreasing with movement of said armature toward said core at increasing energization of said coil, the reluctance between the said one set of laminations and said remaining sets increasing at the movement of said armature toward said core, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature toward said core, means biasing said armature away from said core, the reluctance between said armature and said core increasing with movement of said armature by said biasing means away from said core at decreasing energization of said coil, the reluctance between the said one set of laminations and said remaining sets decreasing with the movement of said armatureaway from said core at the decreasing energization of said coil, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature away from said core.

3. A magnetic circuit comprising a core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the first lamination of said one of said sets stacked in said perpendicular direction, the ux in said magnetic circuit produced at any energization of said coil being a function of practically only the energization current owing in said coil and the reluctance of said magnetic circuit at the beginning of the energization of said coil.

4. A magnetic circuit comprising a core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the first lamination of said one of said sets stacked in said perpendicular direction, the flux in said magnetic circuit produced at any energization of said coil being practically independent of the initial distance between said armature and said core.

5. A magnetic circuit comprising a U-shaped core and an armature, a coil wound around the center leg of said U-shaped core, said core consisting of sets of laminations, the laminations of the center leg of said U-shaped core being stacked with their planes perpendicular to the planes of the laminations of the other legs, the reluctance between said armature and said core decreasing with movement of said armature toward said core at increasing energization of said coil, the reluctance between the said center leg and the other legs of said core increasing at motion of said armature toward said core, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature toward said core.

6. A magnetic circuit comprising a U-shaped core and an armature, a coil wound around the center leg of said U-shaped core, said core consisting of sets of laminations, the laminations of the center leg of said U-shaped core being stacked with their planes perpendicular to the planes of the laminations of the other legs, the reluctance between said armature and said core decreasing with movement of said armature toward said core at increasing energization of said coil, the reluctance between the said center leg and the other legs of said core increasing at motion of said armature toward said core, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature toward said core, means biasing said armature away from said core, the reluctance between said armature and said core increasing with motion of said armature by said biasing means away from said core at decreasing energization of said coil, the reluctance between the said center leg and the other legs of said core decreasing with motion of said armature away from said core, the total reluctance of said magnetic circuit remaining approximately constant with motion of said armature away from said core.

7. A magnetic circuit comprising a U-shaped core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the first lamination of said one of said sets stacked in said perpendicular direction, the flux in said magnetic circuit produced at any energization of said coil being practically independent of the initial distance between said armature and said core.

8. A magnetic circuit comprising a core and a movable armature, a coil wound around a portion of said core, said core consisting of sets of saturable laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the first lamination of said one of said sets stacked in said perpendicular direction, said armature having a plurality of positions with respect to said core, the magnetic flux in said magnetic circuit produced by energization of said coil being practically independent of the position of said armature with respect to said core.

9. A magnetic circuit comprising an E-shaped core and a movable armature, a coil wound around a portion of said core, said core consisting of sets of saturable laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets one end of the laminations of at least one of said remaining sets being positioned adjacent at least a portion of the surface of the rst lamination of said one of said sets stacked in said perpendicular direction, said armature having a plurality of positions with respect to said core, the magnetic ux in said magnetic circuit produced by energization of said coil being practically independent of the position of sad armature with respect to said core.

l0. A magnetic circuit comprising an E-shaped core and a movable armature, a coil wound around the center leg of said E-shaped core, said core consisting of sets of laminations, the laminations of the bridging leg of said E-shaped core being stacked in a direction perpendicular to the direction of stacking of the laminations of the other three legs, said movable armature when at rest being parallel to said bridging leg of said E-shaped core, the flux in said magnetic circuit produced by energizing said coil being independent of the distance between said armature and said core.

11. An electromagnetic relay comprising a magnetic circuit, said magnetic circuit having a core and an armature, a coil wound around a portion of said core, said core consisting of sets of laminations, the laminations of one of said sets being stacked in a direction perpendicular to the direction of stacking of the laminations of the remaining sets, means biasing said armature away from said core, the magnetic pulling force produced by said core on said armature at energization of said coil being essentially a function of the current flowing in said coil and the biasing force of said biasing means.

12. A magnetic circuit comprising a core and an armature, said core being U-shaped and having three legs, the center leg being formed of laminations, a ux source for said magnetic circuit, said laminations in said center leg being stacked in the direction of ow of the magnetic flux at the junctions between said center leg and said other two legs, a coil wound around said center leg, said armature being movable with respect to said core and having a number of intermediate positions between pre-selected limits, the reluctance of said ymagnetic circuit being practically independent of the position of said armature with respect to said core.

13. A magnetic circuit comprising a core and an armae ture, said core being U-shaped and having three legs, a ux source for said magnetic circuit, the center leg being formed of laminations stacked in the direction of ow of the magnetic ux in said core at the junction between said center leg and said other two legs, the other two legs being formed of laminations stacked in a direction perpendicular to the direction of stacking of the laminations in said center leg, said armature being formed of a solid ferro-magnetic substance, a coil wound around said center leg, said armature having a plurality of positions with respect to said core at different energizations of said coil, the reluctance of said magnetic circuit being independent of the position occupied by the said armature with respect to said core.

14. A magnetic circuit comprising a U-shaped core, an energizing winding wound on said core, and an an armature positioned to complete the magnetic circuit of said U-shaped core; said U-,shaped core comprising a rst and second set of laminations; said laminations being electrically insulated from one another, the laminations of said first set of laminations lying in a plane substantially perpendicular to the plane of the laminations of said second set of laminations, said iirst set of laminations having at least a portion of one end thereof positioned adjacent the surface ofthe rst lamination of said second laminations; said armature being movable with respect to the opening formed by said U-shaped core; the reluctance of said magnetic circuit including said U-shaped core and said armature being substantially independent of the position of said armature when said armature is moved between a rst and second position.v

References Cited in the le of patent UNITED STATES PATENTS 1,499,421 Stoekle July l, 19124 1,825,482 Sosinski Sept. 29, 1931 2,330,866 Camner Oct. 5, 1943 2,579,261 Indergand Dec. 18, 1951 2,595,718 Snavely May 6, 1952 2,669,623 MacNeil Feb. 16, 1954 

